1. Field of the Invention
This invention relates to a thermal conductivity detector designed to detect an unbalanced voltage generated in a bridge comprising first through fourth heaters by detecting the thermal conductivity of fluid being examined and supplied to the first and second heaters, the thermal conductivity detector being fit in, for instance, a gas chromatograph and used to measure the concentration of constituents contained in the fluid being examined.
2. Description of Prior Art
FIG. 1 is an explanatory drawing illustrating an example of use of a conventional thermal conductivity detector. In FIG. 1, there are shown first, second, third, and fourth cells 1,2,3,4, respectively, containing first,second, third and fourth heaters 1a,2a,3a, and 4a, respectively. Fluid being examined is led from an inlet 5a (see arrow) of the first cell 1, made to flow through first cell 1 and second cell 2, and led out of an outlet 5b (see arrow) of second cell 2. A reference fluid is led from an inlet 6a (see arrow) of third cell 3, made to flow through third cell 3 and fourth cell 4, and led out of an outlet 6b (see arrow) of fourth cell 4. In addition, first, second, third and fourth heaters 1a,2a,3a and 4a, are connected to form an electrical bridge 7 and a predetermined current is supplied from a constant current supply 8 to bridge 7.
When an unbalance voltage is generated in bridge 7, a detection circuit 9 will detect such unbalance voltage, and in that way, variation in thermal conductivity of the fluids being examined can be measured. Moreover, first, second, third, and fourth cells 1,2,3 and 4, may be of any of the following types: direct flow type cells, shunt direct type cells, diffusion type cells, or semi-diffusion type cells.
Although the use of the direct flow type cell quickens detection response, one disadvantage to such direct flow type cell is that such cell is too sensitive and responds to fluctuations in the quantity of the flowing fluid being examined and the reference fluid. Thus, noise is allowed to be readily generated.
On the other hand, although diffusion type cells do not generate much noise in a detected signal despite fluctuations in the flowing quantities as described above, use of diffusion type cells is disadvantageous because detection response is slow and a sudden change in the thermal conductivity of the fluid being examined cannot be readily followed up.
For these reasons, either type of cells must be selected depending on the intended use. At the same time, generally unsuccessful attempts have been heretofore made, to introduce a thermal conductivity detector which is quick in detection response and which is capable of suppressing such noise. Thus, there is a need in the art for an improved detector having quick response without any substantial noise problem.